The inventive subject matter relates to power systems and methods and, more particularly, to fault detection in power systems using DC power sources.
Power conversion systems that are used to serve AC loads often include an inverter that generates an AC output from a DC voltage provided by a power source. For example, uninterruptible power supply (UPS) systems, which are used to provide uninterrupted power in critical applications, commonly use a battery or other DC power source to provide backup power to an inverter in the event of the failure of a primary power source, such as an AC utility source. Converters used to interface photovoltaic panels to AC power distribution systems also commonly include an inverter that operates off of DC power provided by the photovoltaic panels. Some UPS systems may also be designed to provide power to AC loads from photovoltaic panels, as described, for example, in U.S. patent application Ser. No. 12/779,522, filed May 13, 2010.
In many such applications, the DC power source may be operated such that it “floats” with respect to a system ground. However, ground faults may occur in such systems due to environmental contamination, electrolyte leakage, impact damage and/or other events. Such ground faults may pose operational and safety problems. Techniques for detecting and dealing with ground faults in battery and photovoltaic systems are described, for example, in U.S. Pat. No. 6,593,520, U.S. Pat. No. 6,320,769, U.S. Pat. No. 7,079,406, U.S. Pat. No. 6,856,497, U.S. Pat. No. 7,005,883 and U.S. Pat. No. 6,930,868.